Worms crawling under skin
You could use the Vertex Weigh Proximity modifier to control displacement.
It will use the actual shape of the mesh to correctly displace the surface.



Create a new vertex group in your "skin" mesh and add all vertex to it with a strength of $1$. Now add a new Vertex Weigh Proximity modifier, pick that vertex group, set the "Worm" mesh as Target Object and make sure to set the Distance Mode to Geometry.



After that add a Displacement modifier with weight affected by the previously mentioned vertex group. No texture is required (although you can optionally add one), just adjust strength and displacement distance values as necessary.



You can move your worm mesh around and it will deform according to both position and shape.